Radio frequency receiver and radio frequency transmitter

ABSTRACT

A radio-frequency receiver. The radio-frequency receiver includes a first and second low noise amplifier (LNA), a local oscillating module, and a first, second, and third mixer. The first LNA amplifies a first RF signal. The local oscillating module generates a first, second and third local oscillating signals. The first local oscillating signal is generated according to the second local oscillating signal. The first mixer mixes the first RF signal with the first local oscillating signal to generate an intermediate frequency signal. The second LNA amplifies a second RF signal. The second and third mixers can be operated in two modes. The second and third mixers mix the intermediate frequency signal to generate a first and second baseband signal respectively in the first mode, and the second and third mixers mix the second RF signal with the second and third oscillating frequency respectively in a second mode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/382,108, filed May 8, 2006, and entitled “Radio Frequency Receiverand Radio Frequency Transmitter”.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communications and, moreparticularly, to wideband wireless communication system.

Advances in communication technology have led to an increase in thepopularity of wireless communication. Today, various efforts are underway to apply wireless communication to replace attachment networkingcables used for connecting clients, servers and the like. Examples oftechnology to accomplish wireless networking include the differentvariants of the IEEE 802.11 standard, 802.11a, 802.11b and 802.11g.

For some applications, it is desirable for a device to be able tooperate in multiple wireless protocols. However, the need cannot be metby simply providing the device with multiple transceivers, one for eachprotocol. Sharing core elements of the communication devices is a commonmeans of reducing the area of those communication devices.

The radio frequency of 802.11a uses the 5 GHz spectrum, and the radiofrequency of 802.11b/g operates in the 2.4 GHz spectrum. To receive awide range of these radio signals, a well-designed voltage-controlledoscillator (VCO) or a VCO bank including VCO couples is required. FIG. 1shows a block diagram of a conventional transceiver covering threewireless network standards 802.11a/b/g. The VCO bank usually consists of2 or more VCOs to cover the spectrum of the radio frequencies, hence,the area is increased.

BRIEF SUMMARY OF THE INVENTION

Accordingly, a radio-frequency receiver for wideband with only one VCOis provided. The radio-frequency receiver comprises a first and secondlow noise amplifier (LNA), a local oscillating module, and first,second, and third mixers. The first low noise amplifier (LNA) amplifiesa first RF signal. The local oscillating module generates a first,second and third local oscillating signals. The first oscillating signalis generated according to the second signal, and the second and thirdlocal oscillating signals have a phase difference of about 90 degrees.The first mixer mixes the first RF signal with the first localoscillating signal to generate an intermediate frequency signal. Thesecond LNA amplifies a second RF signal. The second and third mixers arecoupled to the first mixers, and configured in two modes. The second andthird mixer mixes the intermediate frequency signal to respectivelygenerate a first and second baseband signals in a first mode. The secondand third mixers mix the second RF signal with the second and thirdoscillating frequency respectively in a second mode.

The invention further provides a radio-frequency transmitter. Theradio-frequency transmitter comprises a first, second and third mixers,a local oscillating module, a first and second amplifier, and acombiner. The first and second power amplifiers amplify first and secondbaseband signals, wherein the phase difference of the first and secondbaseband signal is about 90 degrees. The local oscillating modulegenerates first, second and third local oscillating signals, wherein thethird oscillating signal is generated according to the second signal,and the first and second local oscillating signals have a phasedifference about of 90 degrees. The first and second mixers mix thefirst and second baseband signals with the first and second localoscillating signal respectively to generate a first and secondintermediate frequency signals. The combiner combines the first andsecond intermediate frequency signal into an intermediate frequencysignal. The third mixers coupled to the combiner mixes the intermediatefrequency signal with the third oscillating signal to generate a firstRF signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more fully understood from the detaileddescription, given herein below, and the accompanying drawings. Thedrawings and description are provided for purposes of illustration only,and, thus, are not intended to be limiting of the present invention.

FIG. 1 shows a block diagram of conventional transceiver covering threestandards 802.11a/b/g;

FIG. 2 shows a block diagram of a radio-frequency receiver according toan embodiment of the invention;

FIG. 3 shows a local oscillating module according to an embodiment ofthe invention;

FIG. 4 shows another embodiment of the local oscillating module;

FIG. 5 shows yet another embodiment of the local oscillating module;

FIG. 6 shows a radio-frequency transmitter according to an embodiment ofthe invention; and

FIG. 7 shows another embodiment of an RF receiver.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 a shows a radio-frequency receiver according to an embodiment ofthe invention. The radio-frequency receiver comprises a first and secondlow noise amplifier (LNA) 202 and 210, a local oscillating module 212, aswitch 214 and a first, second, and third mixers 204, 206, and 208. Thefirst LNA 202 amplifies a first RF signal. The first mixer 204 iscoupled to the first LNA 202. The local oscillating module 212 generatesa first, second and third local oscillating signals, LO₁,LO_(2I)/LO_(I), and LO_(2Q)/LO_(Q), while the phase difference betweenthe second and third local oscillating signals is about 90 degrees. Inthis embodiment of the invention, the second oscillating signal is an I(in-phase) oscillating signal, and the third oscillating signal is a Q(quadrature) oscillating signal, while in other embodiments of theinvention, the second oscillating signal is a Q oscillating signal, andthe third oscillating signal is an I oscillating signal. The localoscillating module 212 mixes the first RF signal with the first localoscillating signal LO₁ to generate an intermediate frequency signal. Thesecond and third mixers 206 and 208 coupled to the local oscillatingmodule can be operated in two modes. In a first mode, the switch 214connects with node A, and the second and third mixer 206 and 208 mixesthe intermediate frequency signal to respectively generate a first andsecond baseband signals. In the second mode, the switch 214 connectswith node B, and the second and third mixers 206 and 208 respectivelymix a second RF signal with the second and third oscillating frequencyLO_(2I)/LO_(I) and LO_(2Q)/LO_(Q), where the second RF signal isreceived and amplified by the second LNA 210. The first, second, andthird mixers in this embodiment of the invention are single-side bandmixers, while in another embodiment of the invention, the first, secondand third mixers can be double-side band mixers.

The switch 214 is optional. Three nodes of switch 214 can be connectedtogether, as shown in FIG. 2B.

In this embodiment of the invention, the first RF signal isdown-converted to intermediate frequency, and then down-converted tobaseband signals. The second RF signal is converted directly tobaseband.

FIG. 3 shows an embodiment of the local oscillating module 212. In thisembodiment of the invention, the local oscillating module 212 comprisesa controllable oscillator 302, a first and second frequency divider 304and 306, and a mixer 308. The controllable oscillator 302 generates anoriginal oscillating signal. The first frequency divider 304 divides theoriginal oscillating signal by a factor of N to generate a first and asecond frequency-divided oscillating signal. The second frequencydivider 306 divides the original oscillating signal by a factor M togenerate the second and third oscillating signals. The mixer 308 mixesthe frequency-divided oscillating signals with the second and the thirdoscillating signal to generate the first oscillating signal. Thefrequency of the original oscillating signal is less than the first RFsignal but excesses the second RF signal.

In a preferred embodiment of the invention, the first RF signal may an802.11a RF signal, and the second RF may be an 802.11b/g RF signal,which means the RF receiver provided by the invention can meet802.11a/b/g specifications with only one oscillator. Besides, bycarefully choosing the original oscillating frequency, the RF receiverdoes not require an image rejection filter. Furthermore, the onlyoscillator does not have to work in a wild range. For example, thefactor M of the local oscillation module in FIG. 3 is s to 2 and N isset to 4. When operated in 802.11a mode, the original oscillatingfrequency can be selected to be 4/5 times of RF signal, which is fromabout 3936 MHz to 4660 MHz. Table 1 shows examples of frequency planningreceived RF frequency, VCO frequency, LO₁, LO_(2I/2Q). For 802.11b/gwith same configuration of local oscillating module, the received RFfrequency ranges from 2400 to 2500 MHz, and the VCO frequency can beselected to be 2 times of received RF frequency. Table 2. shows exampleof frequency planning received RF frequency, VCO frequency, LO_(1/Q).Thus, the total range the VCO has to provide is from 3936 MHz to 5000MHz and the tuning range of the VCO is

$\begin{matrix}{\frac{\left( {5000 - 3936} \right)}{\left( {5000 + 3936} \right)/2} = {23.8{\%.}}} & (1)\end{matrix}$

Therefore, by carefully arranging the frequencies within the RFreceiver, one VCO with small tuning range supporting both 802.11 and802.11b/g can be realized.

TABLE 1 Examples of frequency planning of 802.11 a. RF frequency VCOfrequency LO₁ frequency LO_(2I/2Q) frequency 4920 3936 2952 1968 51504120 3090 2060 5825 4660 3495 2330

TABLE 2 Examples of frequency planning of 802.11b/g. RF frequency VCOfrequency LO_(I/Q) frequency 2400 4800 2400 2500 5000 2500

FIG. 4 shows another embodiment of the local oscillating module 212. Inthis embodiment of the invention, the local oscillating module 212comprises a controllable oscillator 402, a first and second frequencydivider 404 and 406, and a mixer 408. The controllable oscillator 402generates an original oscillating signal. The first frequency divider404 divides the original oscillating signal by a factor of N to generatethe second and the third oscillating signals LO_(2I)/LO_(I) andLO_(2Q)/LO_(Q). The second frequency divider 406 divides the secondoscillating frequency signal by a factor of M to generate a first and asecond frequency-divided signal. The mixer 408 mixes the secondoscillating signal LO_(2I)/LO_(I) with the frequency-divided signals togenerate the first oscillating signal LO₁. In this embodiment of theinvention, the factor M is 2, and the factor N is 2.

FIG. 5 shows yet another embodiment of the invention. In this embodimentof the invention, the local oscillating module comprises a controllableoscillator 502, a first, second, and third frequency divider 504, 506,and 508, and mixers 510 and 512. The controllable oscillator 502generates an original oscillating signal. The local oscillating modulecan be operated in two modes. When operated in the first mode, the thirdfrequency divider 508 and mixer 510 are not activated. The firstfrequency divider 504 divides the original oscillating signal by L togenerate the second and third oscillating signals LO_(2I)/LO_(I) andLO_(2Q)/LO_(Q) the first mode. The second frequency divider 506 coupledto the first divider divides the second oscillating signalLO_(2I)/LO_(I) by M to generate a first frequency-divided oscillatingsignal. Mixer 512 coupled to the first and second frequency dividersmixes the second oscillating signal LO_(2I)/LO_(I) and firstfrequency-divided oscillating signal to generate the first oscillatingsignal LO₁. When operated in the second mode, all the elements of thelocal oscillating module 212 are activated. In the second mode, thesecond frequency divider 506 and mixer 512 operate the same as in thefirst mode. The first frequency divider 504 generates a firstfrequency-dividing oscillating signal. The third frequency dividercoupled to the second frequency divider 508 divides the firstfrequency-divided oscillating signal by N to generate a secondfrequency-divided oscillating signal. Mixer 510 coupled to the first andthird frequency divider mixes the first frequency-divided oscillatingsignal and the second frequency-divided oscillating signal to generatethe second and third oscillating signals LO_(2I)/LO_(I) andLO_(2Q)/LO_(Q).

In a preferred embodiment of the invention, the factors L, M, and N are2, 2, and 2. When operated in 802.11a mode, the original oscillatingfrequency can be selected to be 4/5 times of RF signal, which is betweenabout 3936 MHz to 4660 MHz, as shown in Table 1. For 802.11b/g with sameconfiguration of local oscillating module, the received RF frequencyranges 2400 to 2500 MHz, and the VCO frequency can be selected to be 8/5times of received RF frequency. Table 3. shows example of frequencyplanning received RF frequency, VCO frequency, LO_(1/Q).

TABLE 3 Examples of frequency planning of 802.11b/g. RF frequency VCOfrequency LO_(I/Q) frequency 2400 3840 2400 2500 4000 2500

FIG. 7 shows another embodiment of an RF receiver. The RF receiverincludes two receiver portions 700 and 701 and a local oscillatingmodule 212. The RF receiver can be used for receiving a first RF signal704 in a first mode and for receiving a second RF signal 706 in a secondmode. The first RF signal is, for example, an 802.11a RF signal and thesecond RF signal is, for example, an 802.11b/g RF signal. Theimplementation of local oscillating module can be as same as the localoscillating module 212 in either FIG. 3, 4 or 5. In this embodiment, theoscillating module 212 in FIG. 4 is employed. Note that in thisembodiment of the invention, one VCO (a type of controllable oscillator)is enough to generate all local oscillating signals (LO_(I), LO_(Q),LO₁, LO_(2I), and LO_(2Q)).

In the first mode, the VCO 402 generates an original oscillating signal410. The original oscillating signal 410 is divided by a factor N togenerate frequency-divided oscillating signals (LO_(2I) and LO_(2Q)).Frequency-divided oscillating signals LO_(2I) and LO_(2Q) have a phasedifference about 90 degrees. Frequency-divided oscillating signals(LO_(2I) and LO_(2Q)) are further divided by a factor M to generatefrequency-divided oscillating signals 412. Frequency-divided oscillatingsignals (LO_(2I) and LO_(2Q)) and frequency-divided oscillating signals412 are mixed by a mixer 405 to generate the local oscillating signalLO₁. The mixer 408 is a single side band mixer in this embodiment.

The first RF signal 704 is received and mixed with the local oscillatingsignal LO₁ by a mixer 716 to generate an intermediate frequency signal736. The intermediate frequency signal 736 is mixed by mixers 718 and720 to generate base band signals 732 and 734 respectively.

Jointly referring FIG. 4 and FIG. 7, in the second mode, the VCO 402generating an original oscillating signal 410. The original oscillatingsignal 410 is divided by a factor N to generate frequency-dividedoscillating signals (LO_(I) and LO_(Q)). Frequency-divided oscillatingsignals LO_(I) and LO_(Q) have a phase difference about 90 degrees.

The second RF signal 706 is received and mixed with the localoscillating signal LOI by a mixer 724 to generate a base band signal728. The second RF signal 706 is also mixed with the local oscillatingsignal LOQ by a mixer 726 to generate a base band signal 730. In thesecond mode, the mixer 408 is not activated.

Therefore, only one VCO 708 is needed for both receiver portions 700 and701 to receive different RF signals 704 and 706. In this embodiment, thefactors M and N are selected to be 2 and 2 respectively. However, otherM and N factor values are possible if the frequencies within the RFreceiver are well planned.

FIG. 6 shows a radio-frequency transmitter according to an embodiment ofthe invention. The radio-frequency transmitter 60 comprises a first,second, and third mixer 606, 608, and 604, a local oscillating module612, a first and second amplifier 610 and 602, and a combiner 616. Thefirst and second mixer 606 and 608 respectively receives first andsecond baseband signal. The local oscillating module 612 generates afirst, second and third local oscillating signals LO₁, LO_(2I)/LO_(I),and LO_(2Q)/LO_(Q), wherein the first local oscillating signal LO₁ isgenerated according to the second local oscillating signalLO_(2I)/LO_(I), and the first and second local oscillating signalsLO_(2I)/LO_(I), have a phase difference of about 90 degrees. The firstand second mixers 606 and 608 respectively mixes the first and secondbaseband signal with the first and second local oscillating signalLO_(2I)/LO_(I) and LO_(2Q)/LO_(Q) to generate first and secondintermediate frequency signals. The combiner 616 combines the first andsecond intermediate frequency signal into third intermediate frequencysignal. The third mixers 604 coupled to the combiner 616 mixes the thirdintermediate frequency signal with the third oscillating signal togenerate a first RF signal.

In some embodiments of the invention, the block diagram of the localoscillating module 612 is substantially the same as shown in FIGS. 3,and 4. In other embodiments of the invention, the block diagram of thelocal oscillating module 612 is substantially the same as shown in FIG.5, except when operating in the first mode, the local oscillating module612 generates the LO_(2I), LO_(2Q) and LO₁ as the first, second, andthird local oscillating signal, and when operating in the second mode,the local oscillating module 612 generates the LO_(I), LO_(Q) and LO₁ asthe first, second, and third local oscillating signal. The switch 614 isoptional. In another embodiment of the invention, three nodes of switch614 can be connected together, as shown in FIG. 6B.

Similarly with the receiver, in a preferred embodiment of the invention,the first RF signal may an 802.11a RF signal, and the second RF may bean 802.11b/g RF signal, which means the RF receiver provided by theinvention can meet 802.11a/big specifications with only one oscillator.Moreover, by carefully choosing the original oscillating frequency, theRF receiver does not require an image rejection filter. Furthermore, theoscillator does not have to work in a wide range. The originaloscillating frequency is between about 3700 MHz to 4700 MHz, which isabout 20% tuning range when M and N are both set to 2.

While the invention has been described by way of example and in terms ofpreferred embodiment, it is to be understood that the invention is notlimited thereto. To the contrary, it is intended to cover variousmodifications and similar arrangements (as would be apparent to thoseskilled in the art). Therefore, the scope of the appended claims shouldbe accorded the broadest interpretation so as to encompass all suchmodifications and similar arrangements.

1. A radio-frequency transmitter for operating in a first mode and asecond mode, the radio-frequency transmitter comprising: a first andsecond power amplifiers amplifying a first and second RF signals; alocal oscillating module generating a first, second and third localoscillating signals, wherein the third local oscillating signal isgenerated according to the first and the second local oscillatingsignals, and the first and second local oscillating signals have a phasedifference of about 90 degrees; a first and second mixers mixing a firstand second baseband signals with the first and second local oscillatingsignal, respectively, to generate first and second intermediatefrequency signals; a third mixer for mixing a third intermediatefrequency signal with the third local oscillating signal in the firstmode to generate the first RF signal, wherein the third intermediatefrequency signal is the result of combing the first and secondintermediate frequency signals, and the third intermediate frequencysignal serves as the second RF signal in the second mode.
 2. Theradio-frequency transmitter as claimed in claim 1, wherein the localoscillating module further comprises: a controllable oscillatorgenerating an original oscillating signal; a first frequency dividerdividing the original oscillating signal by a factor of N to generate afirst and second frequency-divided oscillating signal; a secondfrequency divider dividing the original oscillating signal by a factor Mto generate the first and second local oscillating signals; and a fourthmixer mixing the first and second frequency-divided oscillating signalswith the first and second local oscillating signals to generating thethird local oscillating signal.
 3. The radio-frequency transmitter asclaimed in claim 2, wherein the factor M is
 2. 4. The radio-frequencytransmitter as claimed in claim 2, wherein the factor N is
 2. 5. Theradio-frequency transmitter as claimed in claim 1, wherein the localoscillating module further comprises: a controllable oscillatorgenerating an original oscillating signal; a first frequency dividerdividing the original oscillating signal by a factor of N to generatethe first and second local oscillating signals; a second frequencydivider dividing the second oscillating frequency signal by a factor ofM to generate a first and a second frequency-divided signal; and a mixermixing the first and second local oscillating signals with the first andsecond frequency-divided signals to generate the third local oscillatingsignal.
 6. The radio-frequency transmitter as claimed in claim 1,wherein the local oscillating module further comprises: a controllableoscillator generating an original oscillating signal; a first frequencydivider dividing the original oscillating signal by L to generate afirst and second oscillating signals to serve as the first and secondlocal oscillating signals in the first mode; a second frequency dividercoupled to the first frequency divider, dividing the first oscillatingsignal by M to generate a first frequency-divided oscillating signal; athird frequency divider coupled to the second frequency divider,dividing the first frequency-divided oscillating signal by N to generatea second frequency-divided oscillating signal; a fourth mixer coupled tothe first and second frequency dividers, mixing the first oscillatingsignal and the first frequency-divided oscillating signal to generatethe third local oscillating signal; a fifth mixer coupled to the firstand third frequency dividers, mixing the first and second oscillatingsignals with the second frequency-divided oscillating signal to generatethe first and second local oscillating signal in the second mode.
 7. Theradio-frequency transmitter as claimed in claim 6, wherein L, M, and Nis 2, 2, and
 2. 8. The radio-frequency transmitter as claimed in claim1, wherein the frequency of the original oscillating signal is less thanthe first RF signal but exceeds the second RF signal.
 9. Theradio-frequency transmitter as claimed in claim 1, wherein the first,second, and third mixers are single-side band mixers.
 10. Theradio-frequency transmitter as claimed in claim 1, wherein the first RFis an 802.11a RF signal, and the second RF is an 802.11b/g RF signal.11. The radio-frequency transmitter as claimed in claim 1, wherein thefrequency of the original oscillating frequency is between about 3840MHz to 4660 MHz.